PTT, sometimes also called push-over-cellular (=PoC), allows a user of an enabled device to transmit a message, in particular a voice message, instantly and simultaneously to one or more other users of PTT-enabled devices. It is often compared to a walkie-talkie with a vastly extended coverage area, thanks to the use of cellular or wireless telecommunication networks. Today, there are discussions to implement PTT functionality in IP-phones and other mobile devices (IP=Internet Protocol). The “always-on” function of the General Packet Radio Service (=GPRS) permanently keeps up the connection in the background to provide for a swift dial-up. The user's voice message is converted to a data stream and usually transported across a mobile operator's data network to a PTT server, using standard Voice over Internet Protocols (=VoIP). From there, the data streams are forwarded to the receiving users.
US 2004/0192364 A1 describes the provision of a PTT service between a wireless phone locally registered for a PTT service and a PTT-enabled computer that is not registered with any network operator's PTT service. The unregistered network computer with PTT functionality has its PTT address recorded with a Directory Service and is assigned a unique ID by the Directory Service. Then a PTT connection can be established by entering the unique ID at the wireless phone. A PTT server upon reception of the unique ID queries a PTT address for the destination computer from the Directory Service and forwards the PTT request to the unregistered computer. Thus, the number of available PTT destinations is expanded to devices unregistered to a PTT service.
Generally, PTT services are similar to Voice Instant Messaging which is a voice enabled IM solution for conducting IM connections from any wireless or wire-line phone, via voice (IM=Instant Messaging). Users can find out which of their buddies are online, record and send voice instant messages to individuals or buddy groups, and listen to incoming messages that are converted to text and read by an application. To ensure immediate communication, Voice Instant Messaging utilizes standard protocols such as SIP and RTP (SIP=Session Initiation Protocol; RTP=Real-Time Transport Protocol).